A Comparative Study of Carbon Surface Modification Routes: Gamma Irradiation and Aqueous Oxidation using H2O2 for Advanced Carbon/MnO2 Nanocomposite Supercapacitor Electrode

Abstract

Supercapacitors have emerged as attractive energy storage devices due to their fast charging, long cycle life, and high-power density. However, their relatively low energy density remains a challenge, requiring optimization of electrode materials, particularly by increasing oxygen functional groups to improve specific capacitance. In this study, porous carbon derived from palm kernel shells (CPKS) was modified using two methods: conventional treatment using aqueous oxidation with 15% H2O2 (CPKS-h) compared with gamma irradiation (CPKS-i). MnO₂ was subsequently incorporated into both modified carbons via vacuum-assisted wet impregnation, yielding CPKS-h/MnO₂ and CPKS-i/MnO₂ nanocomposites. The samples were characterized using N₂-sorption analysis, FTIR, XRD, SEM-EDX, and TGA. The results showed that gamma irradiation better preserved the porous structure, with only a 0.99% reduction in surface area compared to 1.30% for aqueous oxidation. Both methods also increased oxygen functional groups on the carbon surface, as confirmed by FTIR and SEM-EDX analyses. Electrochemical performance was evaluated using cyclic voltammetry in a three-electrode system. Among the samples, CPKS-i/MnO₂ exhibited the best performance, achieving a specific capacitance of 521.92 F·g⁻¹ at 5 mV·s⁻¹, along with an energy density of 104.38 Wh·kg⁻¹ and a power density of 1.57 kW·kg⁻¹, outperforming CPKS-h/MnO₂. This enhanced performance is attributed to the preserved pore structure and improved surface chemistry induced by gamma irradiation, which enabled more uniform MnO₂ dispersion and promoted a synergistic combination of EDLC and pseudocapacitive mechanisms for efficient charge storage. Thus, gamma irradiation–based carbon modification combined with MnO₂ compositing offers a promising route for advancing supercapacitor research